Referring to FIGS. 10A and 10B that illustrate construction of an information recording and playback apparatus using magnetism, a description of the outline of its structure is first given. FIG. 10A is a plan view of an information recording and playback apparatus as viewed from above. FIG. 10B is a cross-sectional view of the information recording and playback apparatus of FIG. 10A cut along the line A-B-C-D. In FIGS. 10A and 10B, in housing 18 of information recording and playback apparatus 1, a spindle motor for rotating information recording medium 2a and magnetic head actuator 17 for driving magnetic head arm 16 to which magnetic head 15 for movably writing and reading out information signal on a recording surface of information recording medium 21 is attached are secured, and cover 19 hermetically seals the inner part of the case of information recording and playback apparatus 1. A rotor structure is constructed in a manner such that a spindle section consisting of spindle 12 and hub 11 and annular information recording medium 21 having a recording layer of a magnetic substance on the surface are bonded together, and the spindle section is rotatably supported by spindle 12 that is securely disposed at the center of a circular recess of base section 3, bearing sleeve 9, and thrust support plate 10. Hub 11 is secured to spindle 12 by press-fitting or with an adhesive, annular information recording medium 21 is placed on a platform extending outwardly of hub 11 and fixed to spindle 12 with disc-shaped pressure plate 13 and set screw 14. Annular rotor yoke 4 and annular rotating magnet 5 magnetized to a plurality of poles are securely disposed along the circumference on the center side of the bottom surface of the platform of hub 11 on which information recording medium 21 is placed. Stator 8 formed of iron core 6 and coil 7 in the inner periphery of a circular recess of base section 3 is securely disposed opposite to rotating magnet 5, thus building a spindle motor for rotating information recording medium 2a that consists of an integral spindle section and a recording section. FIG. 10C is an illustration of another embodiment of an information recording and playback apparatus, where rotor yoke 4 and rotating magnet 5 are securely disposed along the circumference of the outer periphery of the bottom surface of the platform of hub 11 on which information recording medium 2a is placed. This structure is the same as that of FIG. 10B with the exception that stator 8 composed of iron core 6 and coil 7 is securely disposed on bearing sleeve 9 that is fixed to the center of base section 3 opposite to rotating magnet 5. A spindle motor having the structure as shown in FIG. 10B is generally called an inner-rotor type rotor, whereas a spindle motor having the structure as shown in FIG. 10C is called an outer-rotor type rotor. There are many examples of achieving a thinner design of a spindle motor by providing a hub for securing an annular substrate, namely, information recording medium, on the spindle section of a spindle motor of an information recording and playback apparatus, and providing a rotor magnet and a stator on the periphery of the hub as has been described above.
Also, technologies have heretofore been proposed for preventing malfunctioning of an information recording and playback apparatus due to adherence onto the surface of the recording medium of various gases or particulates emitted by structural materials of an information recording and playback apparatus, and for preventing performance reduction of the recording medium due to chemical reaction of the above-mentioned various gases or particulates with the recording medium (for example, Japanese Patent Application, Publication No. JP59-221845).
However, the heretofore proposed technologies to combat malfunctioning of a conventional information recording and playback apparatus due to adherence on the surface of the recording medium of various gases and particulates emitted by structural materials of the information recording and playback apparatus, or reduction in performance of the recording medium due to chemical reaction of the above-mentioned various gases or particulates relate to methods for absorbing/adsorbing with a filter provided inside the apparatus or inside the cabinet that houses the apparatus, or discharging to outside with a fan or a pump various gases and particulates emitted by the structural materials when the information recording and playback apparatus is in operation after shipment. These proposed technologies also relate to devices or methods for discharging or exhausting in advance various gases or particulates from the recording medium when manufacturing the recording medium itself. Accordingly, they are not effective in suppressing effects caused on the recording medium by gases or particulates emitted by various components and materials during heating and other operations in the manufacture of structural materials of an information recording and playback apparatus. As a result, when gases emitted from an adhesive material during assembling work in the manufacture of an apparatus reach the surface of the recording medium, pollution and degradation of the information recording layer may be caused thus leaving a problem of possible malfunctioning such as head crash unsolved.
What is more, while extra magnetic flux from a rotating magnet converges in the iron core facing to stator and will not hardly leak out when fully assembled as a drive unit for a recording and playback apparatus, during the rotor assembling process, as there is no iron core, an appreciably high level of magnetic flux leakage that might affect information recording layer of the recording medium occurs. At the same time, there has also been a problem that, when a thermosetting adhesive (including an adhesive that requires both ultraviolet ray and heat) is employed in assembling, the magnetic layer is slightly magnetized due to the influence of both leakage flux from a rotating magnet and heat applied in the manufacturing process, thus disturbing a servo signal prerecorded by magnetic transfer and other method on the recording medium and disabling normal recording and playback operation.